The density of semiconductor devices continues to increase due to decreasing semiconductor feature sizes. In order to minimize chip size, the techniques related to manufacturing process, device physics, and reliability in the field of sub-micron semiconductor devices are continually being challenged, developed, and refined.
The metallization process provides interconnections between contacts within semiconductor devices and between devices and conductive pads. To make electrical connections in smaller and more complex chips, multilevel metal interconnects are formed in the semiconductor process. The metal interconnect may be composed of Al, Ti, Cu, W, or other suitable conductive material or combination. A recess such as hole or via is bored through a dielectric covering a first level layer of metal, or a second level layer of metal. The recess is filled with a conductive material (i.e. Al, Ti, Cu, W). The conductive material in the via provides an electrical connection between the first metal layer and the second metal layer or between any two metal layers.
In VLSI multilevel metallization structures, reliability problems of the via can be associated with the aspect ratio of the via, step conditions of the metallization process and materials used in fabricating the via.
FIG. 1 illustrates a step of a conventional interconnection process etching through a dielectric layer 16 into capping layer 14 for forming a via to the conductive layer 12, which is formed on semiconductor layer 10 having a barrier layer (not shown). Unfortunately it is difficult to precisely etch the capping layer 14 through the dielectric layer 16 without etching the underlaying conductive layer 12. When overetching the conductive layer (i.e. Al) 12, the chemical etchant (i.e. CF.sub.4, CBF.sub.3) reacts with the aluminum layer 12 and produces an AlF series polymer 20 on the walls of the via or the bottom of the via, which has a higher electrical resistance than the aluminum layer 12. The high contact resistance of polymer 20 may induce electrical failure of the via contact. Overetching the aluminum 12 also damages the aluminum layer, which may weaken the electromigration characteristics of the aluminum layer 12.
FIG. 2 illustrates another conventional interconnection process directed to solving the problem of producing the high resistivity AlF series polymer. The conventional process includes the steps of forming an aluminum layer 32 on a barrier layer of a surface of the semiconductor (not shown); forming an intermetallic layer 34 (i.e. titanium aluminum TiAl.sub.3) by heating or annealing a titanium layer to react with the underlying aluminum layer 32; forming a titanium nitride layer 36 on the intermetallic layer 34; depositing an interlevel dielectric layer 38 (i.e. silicon dioxide SiO.sub.2) on the titanium nitride layer 36; etching a portion of the dielectric layer 38; and depositing a titanium layer 42 and a titanium nitride layer 44 as a glue layer or an antireflective coating layer (ARC layer) on the dielectric layer 38 and the whole surface of the via 40 (see for example U.S. Pat. No. 5,360,995). The intermetallic layer 34 may protect the overetching of the aluminum layer 32 because the intermetallic layer 34 can be an overetching stop layer of the aluminum layer. But the intermetallic layer 34 unfortunately has a high resistivity, which is an undesirable characteristic in a semiconductor device. Despite providing improvements in via 40, the via contact still has problems due to resistivity of the contact and electromigration characteristics of the metal line and via.